1. Field of the Invention
The present invention relates to an ultrasonic bonding method and device that bonds a material to a bonding surface by the application of ultrasonic vibration.
2. Description of the Related Art
Ultrasonic bonding devices are widely used to subject electronic components, such as semiconductor devices and piezoelectric elements, to flip-chip bonding onto substrates or the like.
Japanese Unexamined Patent Application Publication No. 2001-44242 discloses an ultrasonic bonding device that bonds a material onto a bonding surface while applying pressing load and ultrasonic vibration to the material. In the ultrasonic bonding device, as shown in FIG. 8, a vibrator 71 is attached to one end of a tapered horn 70 to apply longitudinal vibration in the lengthwise direction of the horn 70. A bonding tool 72 is attached to the horn 70 at an antinode of a standing wave of the longitudinal vibration of the horn 70, and extends in a direction substantially orthogonal to the direction of the longitudinal vibration. A connecting portion 73 is provided at almost the center of the horn 70 to be connected to a pressing means for applying a pressing load. When the horn 70 vibrates, a substantially horizontal vibration is transmitted to a contact portion 72a at the leading end of the bonding tool 72 in contact with a material 74 to be bonded. In this case, the vibration is transmitted to the material 74 by a frictional force produced when the material 74 is pressed by the contact portion 72a of the bonding tool 72.
In the configuration shown in FIG. 8, the transmission of vibration to the material 74 is influenced by the frictional force between the contact portion 72a of the bonding tool 72 and the material 74. For this reason, when the frictional force between the material 74 and a bonding surface 75 is greater than the frictional force between the contact portion 72a of the bonding tool 72 and the material 74, the contact between the contact portion 72a and the material 74 can slip, so that vibration is not sufficiently transmitted to the material 74. As a result, bonding failure occurs. Moreover, since the amplitude of the ultrasonic vibration is low (limited to approximately 0.6 μm), and bonding energy is small, it is difficult to perform bonding in a short time and at ordinary temperatures.
On the other hand, Japanese Unexamined Patent Application Publication No. 2001-110850 discloses an ultrasonic bonding device that prevents a material to be bonded from being displaced from a suction tool in the direction of ultrasonic vibration. That is, as shown in FIG. 9, a chamfered portion 80a is formed beforehand on an upper surface of a material 80 to be bonded, and is brought into contact with chamfered portions 81 a provided on two sides of a bonding tool 81 in the direction of ultrasonic vibration, thereby preventing the displacement of the material 80.
In this case, since the chamfered portion 80a of the material 80 and the chamfered portions 81 a of the bonding tool 81 are in contact with each other, there is no influence of the frictional force, which is different from the device shown in FIG. 8. However, the cost is increased because it is necessary to form the chamfered portion 80a on the material 80 to be bonded. Moreover, the chamfered portions 80a and 81 a are not always in precise contact with each other when drawing the material 80, and the material 80 may tilt. Furthermore, since a great force is applied to the chamfered portion 80a of the material 80, the material 80 may be cracked or chipped.